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Research Presentations
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Next Generation All-Electric Telecommunication Satellites (2011-)
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On-Orbit Servicing of Space Systems (2004-)On-orbit
servicing (OOS) of space systems provides immense benefits by extending
their lifetime through replacement and repairs, and by improving their
performance and enhancing their abilities through upgrades. Refueling
is an important aspect of OOS operations. A future servicing operation
(delivery of fuel and/or upgrades) for a system of multiple satellites
like formation flying spacecraft, constellation clusters, and
fractionated spacecraft, would likely several satellites to be serviced
in a single mission. The primary goal of my doctoral research was to
devise strategies that incur minimum fuel during all orbital transfers
required for a distributed refueling mission for satellites in circular
constellations. In this distributed refueling process, satellites have
the capability of distribute fuel amongst themselves in pairs by
engaging in P2P maneuvers. The problem of determining the optimal
strategy of refueling multiple satellites in a constellation, by
expending minimum fuel during the orbital transfers, is challenging,
and requires the solution of a large-scale optimization problem. Our
research efforts centered around a distributed method of
refueling known as the Peer-to-Peer (P2P) refueling. During
a P2P maneuver, a fuel-sufficient and a fuel-deficient satellite engage
in a rendezvous and exchange fuel. After the fuel exchange, the
maneuvering satellite returns to its original orbital position. A P2P
strategy is a natural choice for distributing fuel in the constellation
as part of a mixed refueling strategy, in which an external refueling
spacecraft replenishes part of the satellites in the constellation. The
satellites that receive fuel distribute it to the other satellites in
the constellation by engaging in P2P maneuvers. My studies have
demonstrated that the mixed refueling strategy is a competitive
alternative to a centralized refueling strategy in which a service
vehicle replenishes the satellites. Two
important contributions of my research efforts are: (1) Egalitarian P2P
(E-P2P) refueling, during which we relax the constraint that requires
an active satellite to return to its original orbital position, and (2)
Cooperative P2P (C-P2P) refueling, during which we allow two satellites
to engage in a cooperative rendezvous for exchanging fuel. Both E-P2P
and C-P2P strategies help in the reduction of fuel expenditure in
refueling missions. In fact, a Cooperative Egalitarian P2P (CE-P2P)
strategy, which incorporates both ideas, yields the least fuel
expenditure among all known P2P refueling missions. The refueling
problem is difficult to solve, because it is NP-hard. In order to
estimate the sub-optimality of solutions, I determined bounds on the
fuel expenditure required for P2P refueling missions. After my doctoral
studies, I extended the work on P2P refueling to the more general case
of servicing, and to the case of low-thrust refueling. |
NextGen En Route Traffic Flow Optimization (2009-2011)I developed cooperative and non-cooperative algorithms for de-conflicting En Route air traffic, by minimizing fuel burn, taking into account factors associated with controller workload. <more details to follow>
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Optimal Loitering Trajectories of a Glider (2008-2009)
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Main Results and Highlights2011[New Concept in Space Operations] <coming up soon>. [New Result in OOS] Demonstrated that low-thrust P2P maneuvers increases the flexibility of refueling missions compared to high-thrust case. 2010 [New Result in Aviation] Three-dimensional conflict resolution can lead to fuel savings for aircraft during their passage through En Route airspace. [New Result in OOS] Demonstrated that low-thrust P2P maneuvers increases the flexibility of refueling missions compared to high-thrust case. 2009 2008
2007 2006 2005 2004 |